What is one reason that Descartes offers for believing that the self is a thinking substance and can exist without a body?

What is one reason that Descartes offers for believing that the self is a thinking substance and can exist without a body?
God has told us that we are minds and not bodies.
I can conceive of myself existing without a body, but I cannot conceive of myself existing without a mind.
I might be dreaming and unaware of it.
I have seen my mind, but not my body.